The present invention relates generally to the art of refrigeration. More particularly, this invention is directed to the modification of a basic heat pump system to additionally accomplish the heating or cooling of a liquid, such as hot water for domestic use or chilled water for off peak cooling. With still more particularity, the present invention relates to an air-to-air or water-to-air heat pump capable of conventional space heating or cooling, heating or cooling a liquid and in which heat for defrost of the outdoor heat exchanger is capable of being supplied entirely from stored previously heated liquid. The present invention is capable of space heating or cooling, utilizing heated or chilled liquid as the heat source or sink. Finally this invention relates to a heat pump system capable of (1) space cooling or (2) space heating, or full capacity, (3) liquid heating or (4) chilling without affecting the condition of an indoor space or (5) simultaneous space cooling and liquid heating, or (6) simultaneous space heating and liquid heating, or (7) defrosting the outdoor coil with a previously heated liquid, or (8) space heating or (9) space cooling using heated or chilled liquid.
The use of heat pumps to provide heated or cooled air to an interior space dependent on refrigerant flow path is well known. The basic elements of such systems include a compressor, an indoor heat exchanger, an outdoor heat exchanger and refrigerant expansion devices. Such heat pump systems are used to heat interior spaces by directing refrigerant from the compressor to be condensed in the indoor heat exchanger, then through an expansion device to the outdoor heat exchanger where the refrigerant is evaporated and directed to the compressor. The system may be used to cool the indoor space by redirecting the flow of refrigerant in the cycle such that the indoor heat exchanger is the evaporator and the outdoor heat exchanger is the condenser. Furthermore, it is known that heat pumps may be used to heat water for hot water storage systems.
One disadvantage, inherent in the operation of air-to-air heat pump systems relates to the build up of frost on the outdoor heat exchanger coil when indoor space heating is called for in the heating season and outdoor ambient conditions are conducive to the buildup of frost on the outdoor coil as heat is extracted from the ambient. When conditions are conducive to frost buildup, moisture is precipitated out of the cool air being drawn over and through the outdoor coil at the coil surface where it solidifies in the form of frost or ice. The build up of frost insulates the heat exchanger coil with the result that the heat exchange capability of the coil is degraded and the ability of the heat pump circuit to deliver heat to heat water and/or a conditioned space suffers markedly. The need for timely and effective defrost of the outdoor coil naturally follows.
A common method of defrosting the outdoor coil in a heat pump circuit is known as reverse cycle defrost which entails reversing the operation of the heat pump system from the space heating mode to the space cooling mode of operation.
The effect of such mode reversal is to direct the hot gas discharged by the compressor within the system directly to the outdoor coil as normally occurs in the space cooling mode, as opposed to directing hot gas to the indoor heat exchanger as normally occurs in the space heating mode. During periods of space heating the indoor coil acts as a condenser and the outdoor coil as the evaporator with the result that heat from the hot refrigerant gas discharged from the compressor is given up to the indoor space while heat is extracted from the outdoor ambient for ultimate use indoors. In current reverse cycle defrost schemes i.e., when a heat pump is shifted to what would normally be a space cooling mode, heat is given up to the outdoor coil, which functions as a condenser, and melts the frost buildup on the coil. Since the indoor coil functions as an evaporator in reverse cycle defrost modes it extracts heat from its surroundings i.e., the heated indoor space. The extraction of heat and the lowering of the temperature of the indoor space is clearly an undesirable result and has previously required the energization of a supplemental heat source, such as electrical resistance heaters or a furnace, while the heat pump system is in the defrost mode. The net result of the use of such supplemental heating is the defrost of the outdoor coil at a coefficient of performance of approximately 1.0. Such supplemental heat is significantly more expensive than the heat provided by the heat pump system just as is the electrical resistance heat utilized to heat water in conventional water heating systems. The three medium heat exchanger provides a direct thermal link between the evaporating refrigerant in the indoor heat exchanger and the previously heated liquid thereby allowing a liquid heated defrost cycle.
Another disadvantage, inherent in the operation of heat pump systems, relates to their inability to meet the total space heating needs during low outdoor ambient temperature conditions. The most common method of supplementing the heating capacity of the heat pump at reduced ambient temperature is the energization of a supplemental heat source, as in the defrost mode, such as electrical heaters or a furnace while the heat pump operates below the space heating balance point. The use of supplemental heating at a coefficient of performance of approximately 1.0 reduces the efficiency of the heat pump system but more particularly requires the electrical utility to meet undesirable peak demands.
In order to provide a more economical system, as well as to conserve energy usage, a number of combined systems have been proposed to provide space heating or cooling, either alone or in conjunction with water heating, or water heating alone. (i.e., U.S. Pat. No. 4,598,557 to Robinson). Another system includes the capability of defrosting the outdoor coil using only stored previously heated liquid as a heat source (i.e., U.S. Pat. No. 4,646,537 to Crawford).
A need still exists in the field of integrated heat pumps for an economical and practical system. The prior art requires complex refrigerant circuits with multiple refrigerant control valves. Major electrical utility studies indicate that a practical load managed heated or chilled water storage system can be introduced into the advanced heat pump design if the design concept is based on the integration of year round domestic hot water heating. A need therefore exists for an integrated heat pump capable of year round domestic hot water heating and utilizing a stored liquid as the source or sink for directly heating or cooling the conditioned space or indirectly, through the refrigerant circuit, defrosting the outdoor coil.